Q.: There has been serious spalling in the stems of precast tees of the ceiling in a cattle carcass cooler. The tees are 18 inches high with rebars located 3 inches, 5 inches and 7 inches from the base. Carcasses are run into the cooler on tracks suspended from the tees. The cooler operates at a freezing temperature of 28 degrees F but while the cooler is being loaded with new carcasses the temperature rises to 40 degrees F. The cooler has been in use for 8 years and, because of the carcasses, the inside atmosphere has had a high humidity.

Recently, in order to bring the temperature down faster, carbon dioxide gas was injected through the doorway. This rapid cooling was done a number of times. Some tees near the doorway have now shattered in long slim fractures resembling those of overloaded columns. It is possible that the tees were overloaded with too many carcasses. Some of the fractures are located as high as the highest rebar. What is the likely cause of the fractures?

A.: The most likely cause is that the carbon dioxide gas rapidly froze the concrete which had probably become thoroughly saturated. The very low temperature of the carbon dioxide gas perhaps caused the beams to freeze at the bottom much faster than at the top, causing the high stresses.